Low Latency 40- and 100-Gbps Ethernet MAC and PHY MegaCore Function User Guide

ID 683628
Date 12/28/2017
Document Table of Contents Conditions Triggering XOFF Frame Transmission

The LL 40-100GbE IP core supports retransmission. In retransmission mode, the IP core retransmits a XOFF frame periodically, extending the pause time, based on signal values.

The TX MAC transmits XOFF frames when one of the following conditions occurs:

  • Client requests XOFF transmission—A client can explicitly request that XOFF frames be sent using the pause control interface signal. When pause_insert_tx is asserted, an XOFF frame is sent to the Ethernet network when the current frame transmission completes.
  • Host (software) requests XOFF transmission—Setting the pause request register triggers a request that an XOFF frame be sent.
  • Retransmission mode—If the retransmit hold-off enable bit has the value of 1, and the pause_insert_tx signal remains asserted or the pause request register value remains high, when the time duration specified in the hold-off quanta register has lapsed after the previous XOFF transmission, the TX MAC sends another XOFF frame to the Ethernet network. While the IP core is paused in retransmission mode, you cannot use either of the other two methods to trigger a new XOFF frame: the signal or register value is already high.
Note: Altera recommends that you use the pause_insert_tx signal to backpressure the remote Ethernet node.
Note: Altera recommends that you set and maintain the value of the retransmit hold-off enable bit at 1 to control the rate of XOFF pause frame transmission.